The present invention relates to a lighting device, in particular a lighting device that may be applied to a shadowless lamp or a portable lighting unit useful in dental or surgical diagnosis.
In dental and surgical diagnosis, shadowless lamps are commonly used for casting appropriate light on and around a working site. For a light source of shadowless lamps, halogen lamps have conventionally been used. The halogen lamps, however, generate heat when electric current flows through the filament, such that the surface temperature of the lamps rises to as high as 200 to 300xc2x0 C., thereby having problems in safety. Such calefacient light also discomforts the patients and doctors. Further, the halogen lamps are not resistant to vibration, short in service life, and expensive.
There has not been known a composite element wherein light emitting diodes are arranged in rows and columns for a lighting purpose.
It is an object of the present invention to provide a lighting device having a light source that is safe, long-life, and low-cost.
According to the present invention, there is provided a lighting device comprising a composite element having a plurality of light emitting diodes arranged in rows and columns.
The composite element is in the form of a plate composed of a plurality of light emitting diodes (referred to as xe2x80x9cLEDsxe2x80x9d hereinbelow) arranged in rows and columns. The shape of the plate is not particularly limited, and may be circular, oval, or polygonal such as rectangular shape. The composite element, compared to the halogen lamps, provides a higher light transforming rate and thus a remarkably less heat release value, thus being safe. In addition, the composite element is free of filaments, which structure results in high impact-resistance and long service life, and realizes light emission at low voltage and current, thus being advantageous in cost.
The lighting device of the present invention may further have heat removing means for removing heat generated by the composite element, and light controlling means for controlling the light paths of the LEDs.
The heat removing means removes the uncomfortable feeling of heat given by the light rays emitted by the LEDs. Examples of the heat removing means for this application include a layer having an infra-red cut-out layer for cutting out at least a portion of the infra-red rays of the light emitted by the LEDs, and a liquid cooling agent for cooling the surface of the LEDs of the composite element. The layer having an infra-red cut-out layer may preferably be a radiator plate that transmits only the infra-red rays, or a special coating that absorbs the infra-red rays. The cooling agent may preferably be a silicon oil.
The lighting device of the present invention may further be provided with a reflector that reflects the light rays emitted by the LEDs of the composite element in the direction of the irradiation. With such a reflector, the present lighting device can be used as a shadowless lamp.